jtaekman, the information you're looking for is in [URL="http://forums.omnigroup.com/showpost.php?p=113714&postcount=18"]this post[/URL]. Hope that helps!

I too am being asked repeatedly for my username and password after upgrading to Mountain Lion. This, along with the broken mail rule under Mountain Lion has made OmniFocus a real mess. I'm disappointed that these issues were not addressed by OmniGroup in the months in which developers could access and test against Mountain Lion.

[QUOTE=Brian;113714]Some customers seeing this have reported that using Keychain Access to remove the entry for sync.omnigroup.com is sufficient to get things back up and running normally, at least temporarily. (We've seen reports of similar keychain-related issues in other apps on Mountain Lion, so our current working theory is that this is something Apple's going to need to address.)[/QUOTE]

This did not solve the problem for me.

[QUOTE=thebd;114835]I too am being asked repeatedly for my username and password after upgrading to Mountain Lion. This, along with the broken mail rule under Mountain Lion has made OmniFocus a real mess. I'm disappointed that these issues were not addressed by OmniGroup in the months in which developers could access and test against Mountain Lion.
[/quote]
You're making a big assumption here, which is that the problem manifested itself during their testing prior to ML's release. You're also assuming that ML has been a stationary target, but it hasn't. For a concrete example that has caused some OmniFocus crashes, see Ken's post [URL="http://forums.omnigroup.com/showthread.php?p=114822"]here[/URL]. No amount of testing against code that is different from what Apple finally releases is going to ensure trouble-free operation!

[quote]
This did not solve the problem for me.[/QUOTE]
Contact the support ninjas directly, and they'll help you track down the problem. Email [email]omnifocus@omnigroup.com[/email], or call 800-315-6664 or +1-206-523-4152 between 10 and 5, Seattle time.

Same issue
 

I have the exact same issue:

Running OF 1.10.3 on OSX 10.8.2 on a latest gen MacBook Air.

This is the first time I have tried to use OF since upgrading to 10.8.2 from 10.8.1. I get the same issue, dialog box for the Sync server keeps popping up. Used the same credentials to log into the website, no problems there.

How do I fix this?

Sorry for the confusion! This appears to be a bug in 10.8 which Apple will need to address in a system update. More information, including a workaround is available in [URL="http://forums.omnigroup.com/showpost.php?p=113714&postcount=18"]this post[/URL].